The invention relates to the charging of an electrical energy storage device of an electric vehicle at a power socket serving as a power supply—particularly a household power socket.
In the following, the term ‘electric vehicles’ means any vehicle which is driven by an electric motor, wherein the electric motor obtains electrical energy from an electrical energy storage device (for example, an electric battery or an electric capacitor) which can be charged at an electric charging source outside the vehicle—for example at a household power socket connected to a power grid. This means both purely electrically-driven electric vehicles with no internal combustion engine, as well as electric vehicles with range extenders and plug-in hybrid vehicles.
Conventional single-phase household power sockets, with 230V alternating current (for example, in Europe) or 120V alternating current (for example, in North America), by way of example, can usually only supply a low maximum charging current—for example a maximum of 16 A—in contrast to industrial power sockets, charging stations, or wall boxes. When the current load is exceeded, an overcurrent protection device is typically triggered, and interrupts the circuit.
In the IEC 61851-1:2010 and SAE-J1772 (January 2010) norms for the standardization of the charging of electric vehicles, it states that the maximum charging current which the vehicle can draw via the external charging source is communicated to the vehicle via the pulse width ratio of the pulse-width modulated pilot signal generated in the power supply device (EV supply equipment)—for example 13A at a certain pulse width ratio. When the vehicle knows the maximum charging current (that is, the available charging current), it can scale up the actual charging current to the same.
In cases where charging occurs at a power socket, the pilot signal which indicates the maximum charging current is generated in a so-called in-cable control box which is part of the charging cable fitting.
According to IEC 61851-1:2010, the current carrying capacity of the charging cable fitting can be coded by the value of a resistor in the charging cable fitting—for example 1.5 kΩ at 13 A current carrying capacity, and 220Ω at 32 A current carrying capacity. This resistor is also called a proximity resistor because it is situated between the proximity contact and the ground contact in the vehicle coupling connected to the vehicle.
It is possible to realize charging cable fittings for different household power socket types with different current carrying capacities using the mechanisms defined to date in the standards for limiting charging current.
Numerous electric vehicles can be charged in a household power socket by means of a mobile charging cable fitting, said power socket being part of an electric circuit which is protected by an overcurrent protection device (for example, a 16 Å circuit breaker), which can also be loaded by additional consumers during charging of the vehicle in addition to the electrical load of the vehicle.
In such cases, it cannot be predicted when, and whether, a consumer is added to the same electric circuit along with the vehicle. If the overcurrent protection device is tripped when a consumer is added to the electric circuit, the overcurrent protection device in the domestic installation interrupts the electric circuit such that the power supply fails and the charging is halted. In the opposite scenario, a load resulting from one consumer or multiple consumers may already be connected to the electric circuit before the load of the electric vehicle is added to the electric circuit, such that the overcurrent protection device is tripped when the electric vehicle is added to the electric circuit for the purpose of charging the motor vehicle, and the overcurrent protection device then immediately cuts the electric circuit.
If the interruption implemented at the overcurrent protection device is manually overridden—for example by the user resetting a circuit breaker, the vehicle will automatically attempt to charge the vehicle again using the same charging current as before the failure of the power supply, and the overcurrent protection device will again interrupt the electric circuit. This repeated tripping of the overcurrent protection device in the domestic installation can lead to damage to electric installations over time. In addition, this means that the user of the electric vehicle cannot charge his vehicle as long as he does not carry out a modification of the loads on the electric circuit—for example by removing a consumer on the electric circuit.
The problem addressed by the invention is that of eliminating the disadvantages described above.
The problem is addressed by the features according to the exemplary embodiments of the invention.
A first aspect of the invention relates to a method for charging an electrical energy storage device of an electric vehicle at a power socket serving as the power supply. The method is preferably used for charging at a household power socket—by way of example at a single-phase 230V or 120V household power socket—because in household power sockets, the overcurrent protection device is triggered even at low charging currents—for example above approx. 14 A continuous current (a breaker with a nominal value of 16 A can trip at approx. 10% below its normal value if there is a continuous current). However, in principle, the invention could also be used for charging at industrial power sockets with higher current protection.
By way of example, the energy storage device of the vehicle has already been charging for a certain period of time, and an overcurrent protection device is triggered by the addition of a further consumer, leading to a failure of the power supply. As an alternative, by way of example, an overcurrent protection device is triggered immediately after charging starts, if, for example, the electric circuit was already loaded by one or multiple consumers.
According to the method, following the failure of the power supply, and subsequent restoration of the power supply, a charging current is used to charge the electrical energy storage device, which is automatically reduced—for example by 10% or more—compared to the charging current prior to the failure of the power supply.
That is, an automatic reduction in charging current following a sudden failure of the power supply is provided according to the invention. If the charging procedure is re-started following the restoration of the power supply, the vehicle charges with a reduced charging current.
Using the method according to the invention, it is possible for a charging process to be continued following the triggering and subsequent reset of the overcurrent protection device in the domestic installation, without the overcurrent protection device being triggered repeatedly. The charging process in this case can be automatically continued at the vehicle end following restoration of the power supply, without the user needing to act. The invention prevents damage to the domestic electrical installation resulting from repeated triggering of the overcurrent protection device in the domestic electric installation. In addition, the invention enables a charging at an electric circuit which is loaded with other electrical consumers, or at an electric circuit which has weak overcurrent protection, without the user needing to carry out a modification of the loads on the electric circuit—for example by removing a consumer from the electric circuit. A user who does not wish to get involved with the current capacity of the domestic installation, or other charging current settings, is freed from these tasks because the charging current is adapted automatically.
Moreover, the method according to the invention reduces the heightened wear of household power sockets and of the plug of the charging cable fitting, the same resulting when, during the charging process, the plug of the charging cable fitting is first pulled out of the power socket, rather than the vehicle coupling of the charging cable fitting being pulled out of the power connector of the vehicle. The removal of the plug from the power socket can be interpreted as a failure of the power supply, such that a reduced charging current is used for a later charging process. In order to prevent a reduction in the charging current, the user first separates the vehicle coupling of the charging cable fitting. This is generally only possible if a release device is actuated which simultaneously ends the charging—such that the power supply contacts of the vehicle coupling of the charging cable fitting carry substantially zero current when released.
The charging current is preferably limited at its upper end by an active charging current limit prior to failure of the power supply and following restoration of the power supply. In the method according to the invention, the active charging current limit in this case is smaller following restoration of the power supply than the active charging current limit prior to the failure of the power supply—particularly by at least 10%. The active charging current limit is, by way of example, reduced from approximately 13 A to approximately 10 A.
The mechanism for the automatic charging current reduction can be implemented, by way of example, in the vehicle, or alternatively in the in-cable control device of the charging cable fitting.
In one embodiment of the method according to the invention, the mechanism for reducing the charging current is implemented in the vehicle—that is, the reduction of the charging current is performed on the vehicle end. For this purpose, there is a variable charging current limit in the vehicle, prior to the failure of the power supply, for the purpose of limiting the maximum charging current for the charging of the household power socket. The variable charging current limit can be modified, by way of example, by the user via an operating element in the vehicle, and corresponds by way of example to a defined fraction of the maximum charging current encoded by the pilot signal—for example a variable charging current limit with multiple steps, for example three steps of 100%, 75%, and 50% of the maximum charging current encoded by the pilot signal. In the event that a failure occurs in the power supply prior to the end of charging, the vehicle automatically reduces the charging current limit; by way of example, in the case of a charging current limit which can be adjusted by multiple steps, the charging current limit is reduced by one step (for example from 100% of the maximum charging current to 75% of the maximum charging current).
Once the power supply has been restored, the charging process is then carried out at a reduced charging current, corresponding to the reduced charging current limit (if the charging process has not been ended).
The reduced charging current limit can be saved in the vehicle such that it can preferably be utilized to limit the charging current for another charging process following use of the vehicle (for example, on the following day).
The charging current limit is reduced in this embodiment following failure of the power supply. The vehicle can recognize the failure of the power supply, by way of example, for the purpose of triggering the reduction of the charging current limit, and can reduce the charging current limit once it has recognized the failure. The failure of the power socket can be determined, by way of example, by the presence of two conditions. First, there is a corresponding signal in a proximity circuit which includes the proximity contact, which indicates an existing connection of the vehicle coupling of the charging cable fitting to the vehicle (by way of example, a certain current is flowing over the proximity resistor on the proximity contact). Second, the vehicle no longer detects a pilot signal.
The reduction of the charging current limit can be repeated—even multiple times. As such, the charging current limit is reduced by a first value, for example, following a first failure of the power supply; after the charging process is resumed and a second failure then occurs in the power supply, the charging current limit is again reduced before the charging process is ended. In addition, a charging current limit which is reduced due to a failure of the power supply is also preferably used upon a new charging process (for example the following day). A failure of the power supply upon the new charging process would then lead to a further reduction in the already-reduced charging current limit.
The vehicle preferably uses a charging current limit present in the vehicle for the purpose of limiting the charging current when the vehicle recognizes that the vehicle is being charged at a household power socket and not at a charging station or a so-called wall box. For this purpose, a test is made, for example of whether the available charging current is less than—or is equal to or less than—a threshold value, for example less than or equal to a threshold value of approximately 15 A (the exemplary threshold value of 15 A is reasonable considering that the charging cable fittings which can be used for household power sockets are generally coded with 12 A as the available charging current). For this purpose, the maximum charging current encoded by the pilot signal, and optionally the current carrying capacity defined by the proximity resistor, can be analyzed. By way of example, the vehicle observes the charging current limit if the maximum charging current defined by the pilot signal, and the current carrying capacity encoded by the proximity resistor, are less than or equal to a threshold value of approximately 15 A, because this indicates charging at a household power socket.
Preferably, a charging current limit which was already reduced is not used in a renewed charging process for the purpose of limiting the charging current, under the condition that the vehicle is not being charged at a household power socket (but rather at a charging station or a so-called wall box). For this purpose, a check is made, by way of example, of whether the available charging current of the power socket is greater than—or is greater than or equal to—a threshold value, wherein this is particularly recognized using the received pilot signal. By way of example, a charging current limit which was already reduced in a previous charging process is ignored in a renewed charging process if the maximum charging current defined by the pilot signal, and optionally also the current carrying capacity encoded by the proximity resistor, are greater than a threshold value of approximately 15 A, by way of example. In this case, the charging current is limited by an active charging current limit which corresponds to the minimum (lesser) of the maximum charging current defined by the pilot signal and the current carrying capacity encoded by the proximity resistor.
In a further embodiment of the method according to the invention, the mechanism which reduces the charging current following a failure of the power supply is implemented in the in-cable control device of the charging cable fitting—that is, the reduction of the charging current is carried out by an in-cable control device of the charging cable fitting.
For this purpose, a reduced charging current limit used to limit the charging current is saved in the in-cable control device prior to the failure of the power supply, wherein this charging current limit is reduced compared to the active charging current limit prior to the failure of the power supply of the motor vehicle. That is, a charging current limit is saved which is less than the charging current limit which was used, up to the failure of the power supply, for the purpose of limiting the maximum charging current. After the power supply is restored, the saved, reduced charging current limit is then used as the active charging current limit for the purpose of limiting the charging current.
The background for the early saving of a reduced charging current limit (for example even before the charging of the vehicle begins) is that the in-cable control device itself is no longer supplied with current upon a failure in the power supply (because it typically does not have its own power supply), and therefore it can no longer react to the failure by reducing the charging current limit.
The charging current limit is preferably saved in the control device non-volatilely by means of a non-volatile memory—for example by means of a flash memory device or an EEPROM (electrically erasable programmable read-only memory). The saved charging current limit is saved permanently as a result of the non-volatile saving of the charging current limit—that is, even if the plug of the charging cable, with the in-cable control device, is separated from the household power socket, and therefore is no longer supplied with current.
A reduced charging current limit is preferably saved after the vehicle signals that it is ready to be charged, and before the charging of the vehicle begins. Pursuant to IEC 61851-1:2010, a switch in the charging interface of the vehicle is closed to signal readiness for charging, such that the high-level of the pilot signal drops from +9V to +6V. This level drop can be recognized by the control device, and then a reduced charging current limit can be saved which is then used following a power failure and subsequent restoration of the power supply for the purpose of limiting the charging current.
The charging process is carried out by way of an active current limit (for example 13A) which is greater than the saved, reduced current limit (for example 10A). If the charging process ends without a failure in grid power, the active current limit is taken as the charging current limit and saved in the control device. In the process, the reduced charging current limit which is preferably saved prior to the start of the charging process is overwritten. If, however, during the charging a grid power failure occurs, the charging process is performed at reduced charging current following restoration of the power supply, because after the control device is switched on, the saved, reduced charging current limit is taken as the active current limit.
It is advantageous if the charging current limit can be set by the user via an operating element of the charging cable fitting, and is preserved when the charging cable fitting is removed from the household power socket. The set charging current limit is taken as the active charging current limit for the purpose of limiting the charging current during the charging process.
A second aspect of the invention relates to an electric vehicle having an electrical energy storage device which can be charged at a household power socket which serves as the power supply, via a charging device integrated in the vehicle. The vehicle has a variable charging current limit for the purpose of limiting the maximum charging current; the charging current limit can preferably be modified by the user. The vehicle is configured to automatically reduce the charging current limit upon a failure of the power supply.
The embodiments above relating to the method according to the invention, according to the first aspect of the invention, apply in an analogous manner to the electric vehicle as well, according to the second aspect of the invention. Advantageous embodiments of the electric vehicle which are not explicitly described correspond to the advantageous embodiments of the method according to the invention described above.
A third aspect of the invention relates to a control device for a charging cable fitting. The control device is configured to save a reduced charging current limit used for the purpose of limiting the charging current before a failure of the power supply, particularly in a non-volatile manner. The reduced charging current limit is lower than an active charging current limit used during charging for the purpose of limiting the charging current prior to the failure of the power supply, such that the saved, reduced charging current limit for the purpose of limiting the charging current is used for the charging process following restoration of the power supply. For this purpose, the saved current limit is preferably taken as the active current limit, and is indicated to the vehicle by the control device, via the pilot signal.
The embodiments above relating to the method according to the invention, according to the first aspect of the invention, also apply in an analogous manner to the control device, according to the third aspect of the invention. Advantageous embodiments of the control device which are not explicitly described at this point correspond to the advantageous embodiments of the method according to the invention described above.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.